Frequency Modulated Continuous-wave (FMCW) radar is a short range measuring radar set. FMCW radar is often used as a “radar altimeter” to measure the exact distance between an aircraft and the ground during landing procedures. With the advent of modern electronics, the use of Digital Signal Processing (DSP) is used for most detection processing. The signals are passed through an Analog to Digital converter (ADC), and digital processing is performed on the result.
Current aircraft radio altimeter installation involves placing two separate antennae on the underside of the aircraft. Siting these antennae, including a transmitting antenna and a receiving antenna, is non-trivial. When the antennae are too far apart, low altitude performance is limited. When the antennae are too close together, the antennae suffer leakage due to poor isolation. Leakage may render the radio altimeter effectively useless if coupling between the antennae cannot be handled by software. Coupling is the transfer of energy from one circuit segment to another through some electrical process such as induction.
Consequently, it would be advantageous if an apparatus existed that is suitable for housing a receiving antenna and a transmitting antenna in close proximity, while limiting coupling between the antennae.